The impact of processing speed on cognition in temporal lobe epilepsy.

Purpose: To characterize the impact of slowed processing speed on the efficiency of broader cognitive function in temporal lobe epilepsy (TLE).

Methods: Participants included 100 patients with TLE and 89 healthy controls (mean ages 36.8 and 33.6, respectively) administered a neuropsychological battery consisting of 15 cognitive metrics. Confirmatory factor analysis using structural equation modeling (SEM) latent variable modeling demonstrated a cognitive structure representing the domains of verbal intelligence, immediate memory, delayed memory, executive function, working memory, and processing speed. Furthermore, the latent variable measurement model determined the direct and indirect relationships of verbal intelligence and processing speed with immediate memory, delayed memory, executive function, and working memory.

Results: Following SEM of hypothesized structural models, the results demonstrated that, among controls, intelligence had a direct and unmediated (by processing speed) relationship with all identified cognitive domains. In contrast, among participants with TLE, processing speed mediated the relationship between verbal intelligence and performance across all cognitive domains.

Conclusion: Slowing of cognitive/psychomotor processing speed appears to play a critical mediating role in the broader cognitive status of participants with TLE and may serve as a target through which to attempt to exert a broad positive impact on neuropsychological status.